Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753126AbbHCKzg (ORCPT ); Mon, 3 Aug 2015 06:55:36 -0400 Received: from mail-wi0-f182.google.com ([209.85.212.182]:34352 "EHLO mail-wi0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753061AbbHCKzf (ORCPT ); Mon, 3 Aug 2015 06:55:35 -0400 Subject: Re: [PATCH 1/2] KVM: x86: set TMR when the interrupt is accepted To: "Zhang, Yang Z" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" References: <1438177055-26764-1-git-send-email-pbonzini@redhat.com> <1438177055-26764-2-git-send-email-pbonzini@redhat.com> <55BB2B62.1030605@redhat.com> <55BF21E1.5030100@redhat.com> Cc: "alex.williamson@redhat.com" , "srutherford@intel.com" , "Gudimetla, Giridhar Kumar" From: Paolo Bonzini X-Enigmail-Draft-Status: N1110 Message-ID: <55BF48A4.5030409@redhat.com> Date: Mon, 3 Aug 2015 12:55:32 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1521 Lines: 39 On 03/08/2015 12:23, Zhang, Yang Z wrote: > > In any case, the TMR behavior introduced by the APICv patches is > > completely different from the hardware behavior, so it has to be fixed. > > But any real problem with it? It is a problem for split irqchip, where the EOI exit bitmap can be inferred from the IOAPIC routes but the TMR cannot. The hardware behavior on the other hand can be implemented purely within the LAPIC. > > The alternative is to inject level-triggered interrupts > > synchronously, without using posted interrupts. > > > > I'll write some testcases to understand the functioning of TMR in the > > virtual-APIC page, but the manual seems clear to me. > > Currently, no existing hardware will use TMR and will not cause any > problem.(That's the reason why we leave it in Xen).But we don't know > whether future hardware will use it or not(SDM always keeps changing > :)). But that would be covered by a different execution control (for backwards compatibility). We'll get there when such a feature is introduced. > And per 24.11.4's description, the perfect solution is don't > modify it. btw, IIRC, only TMR doesn't follow the rule. All other > VMCS accesses are issued in right VMCS context. Yes, that's correct. It's just the TMR. Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/